The present invention is applied to a direct current vibration motor used in an incoming call vibration-generating device for a mobile telephone or the like. More particularly, the present invention relates to a direct current vibration motor suitable for a size reduction and an armature structure thereof.
As a flat-type direct current vibration motor used in a small-size wireless telephone paging device and a mobile telephone, for example, as shown in FIG. 15, there is known a motor in which a rotor has an eccentric structure (Jpn. Pat. Appln. KOKAI Publication No. 6-205565). This vibration motor comprises a stator 102 comprising four permanent magnets 101 arranged in a ring-like configuration and magnetized in an axial direction, and a rotor 104 provided with an armature 103 located opposite to the permanent magnets 101 of the stator 102, wherein the armature 103 of the rotor 104 is constituted in such a manner that the whole armature 103 of the rotor 104 is formed in a fan-like configuration by allowing three coils 105 to which current is supplied to be located adjacent to each other in a circumferential direction with the result that the rotor 104 is formed in an eccentric structure.
When current is supplied to these threes coils 105 via a commutator 106, the rotation direction of the rotor 104 is determined by the Fleming's left hand law with the direction of the current and the direction of the magnetic force from the permanent magnets 101. Current flowing via the commutator 106 is simultaneously supplied to two or more coils 105. At least two coils 105 out of the three coils 105 exceed the other coil 105 so that the restart-up thereof is enabled irrespective of the suspension position of the rotor 104.
A vibration is generated with an eccentric load by the rotation of the rotor 104 by arranging the three coils 105 at an eccentric position deviated to one side of the rotor 104 in this manner. With such three coil motors, even when the direction of the current flowing through the two coils are different, the start-up direction thereof can be made equal by arranging the three coils so that the direction of the magnetic force corresponding to these coils becomes different. As a consequence, the motor can be started up irrespective of the suspension position of the rotor 104.
By the way, along with the prevalence of mobile telephones, a direct current motor smaller in size than the conventional type is desired so that the incoming vibration of the mobile telephones on trains or the like can be felt through a wrist watch or the like worn at all times by men instead of the main body of the mobile telephones. However, with the conventional flat-type direct current vibration motor described above, the rotors are concentrated at one location in a circumferential direction, but three phases coils are arranged in parallel in the circumferential direction so that the rotors inevitably become large in the circumferential direction to some extent and no large eccentric effect can be obtained with the result that the strength of vibration felt by men is limited. Consequently, when an attempt is made to reduce the size of the external diameter of the vibration motor of this type so far commercially sold on the market, there arises a problem in that the function of vibration motor cannot be sufficiently attained.
Therefore, in order to obtain a higher eccentric effect with the small-size motor, there is proposed an eccentric direct current vibration motor in which the armature 202 of the rotor 201 is constituted of one or two coils 203, for example, as shown in FIG. 16 (Jpn. Pat. Appln. KOKAI Publication No. 10-336983). In this motor, the commutator 203 is divided into four in the circumferential direction so that the divided bodies of the commutator located opposite to each other are commonly connected. At the same time, both the start end and the terminal end of the coil are connected to the adjacent divided bodies of the commutator respectively to supply the current to the divided bodies of the commutator via a brush arranged through 90°. When the rotor 201 is rotated, the direction of the current flowing through the coil 203 for each of the rotation angle is reversed, the rotation of the rotor 201 is sustained with the absorption and the repulsion action of the N/S poles of the permanent magnet 101 and the magnetic force of the coil 203.
However, one coil type motor is constituted in a mechanism in which the adjacent divided bodies of the commutator are instantly short circuited with the brush in that the direction of the current flowing through the coil 203 is changed over. In this case, the short circuit of the power source is generated. Consequently, there is provided a non-electrification dead point in which the brush is not connected to any of the commutator so that such short circuit of the power source is not generated. By the way, in the case where the rotor 201 is suspended with this dead point, current does not flow through the coil 203 at the next time of rotation so that the start-up is disabled.
Therefore, in order to secure the start-up by preventing the suspension of the rotor at this dead point, an iron pin 205 formed of a magnetic body is provided which regulates the static position at one part of the armature 202.
However, even when an attempt is made to regulate the start-up position with the iron pin, the presence of the iron pin itself constitutes a rotation load. In addition, when a contact friction resistance between the brush and the commutator exceeds a return force to a normal static position with a magnetic force between the iron pin and a permanent magnet with an increase in the contact friction resistance with the lapse of time, the rotor is suspended at the dead point in the end. Furthermore, when the iron pin is arranged so that a magnetic force sufficiently larger than the friction force can be obtained, the magnetic force of the coil which will start the rotor becomes weaker than the magnetic force between the iron pin and the permanent magnet this time with the result that the start-up incapability is induced. Consequently, there is a problem in that the setting of the pin of the magnetic body and the arrangement thereof are difficult in the method for regulating the rotor to the static position with the pin of the magnetic body.